Quadruple Switching of Pleated Foldamers of Tetrathiafulvalene–Bipyridinium Alternating Dynamic Covalent Polymers

Abstract

Two dynamic covalent polymers P1 and P2 were prepared by alternately linking electron-rich tetrathiafulvalene (TTF) and electron-deficient bipyridinium (BIPY(2+) ) through hydrazone bonds. In acetonitrile, the polymers were induced by intramolecular donor-acceptor interactions to form pleated foldamers, which unfolded upon oxidation of the TTF units to the radical cation TTF(.+) . Reduction of the BIPY(2+) units to BIPY(.+) led to the formation of another kind of pleated secondary structures, which are stabilized by intramolecular dimerization of the BIPY(.+) units. The diradical dicationic cyclophane cyclobis(paraquat-p-phenylene) (CBPQT(2(.+)) ) could further force the folded structures to unfold by including the BIPY(.+) units of the polymers. Upon oxidation of the BIPY(.+) units of the cyclophane and polymers to BIPY(2+) , the first folded state was regenerated. Switching or conversion between the four conformational states was confirmed by UV/Vis spectroscopic experiments.

Bipyridinium radical cation dimerization-driven polymeric pleated foldamers and a homoduplex that undergo ion-tuned interconversion

“…1). 15,19 At the identical concentration of BIPY 2+ (0.2 mM), no such absorption of (BIPY •+ ) 2 was observed in acetonitrile in the spectrum of M1. For all the polymers, the absorption spectrum exhibited the absorption band centred around 650 nm, which corresponded to the monomer BIPY •+ .…”

“…The reduction was realized by the addition of an excess of activated zinc dust to the solution of the polymers in acetonitrile. 15 Thus, the dimerization of the BIPY •+ units in the polymers possessed positive cooperativity, even though it is not clear at this stage that the cooperativity was intra-or intermolecular. 15,19 The spectra also displayed a broad absorption band around 1020 nm, which could be ascribed to the radical cation dimer (BIPY •+ ) 2 .…”

“…7,11g-i β-Sheet is another important secondary structural motif of natural peptides. Currently a number of artificial pleated systems have been constructed by utilizing the donor-acceptor interaction, 13-15 solvophobicity 16 or radical interaction 15,17 as the driving force. Currently a number of artificial pleated systems have been constructed by utilizing the donor-acceptor interaction, 13-15 solvophobicity 16 or radical interaction 15,17 as the driving force.…”

“…The β-sheet subunits in long peptides or proteins can further bind to form supersecondary structures, 12 such as β-meander and Greekkey, which are crucially important for the assembly of higherorder tertiary structures and the generation of many advanced functions. Previously we had reported that bipyridinium (BIPY 2+ )-tetrathiafulvalene alternating polymers form two different pleated conformations driven by the donor-acceptor and bipyridinium radical cation (BIPY •+ ) dimerization, 15 respectively. Further development of tunable pleated systems may lead to potential applications in the design of new smart molecular materials.…”

Dynamic Molecular Metamorphism Involving Palladium‐Assisted Dimerization of π‐Cation Radicals

“…One strategy that we have used over the past few years to circumvent these issues and to promote the formation of intramolecular π‐dimers between viologen cation radicals relies on tedious multistep sequences aiming at introducing suitable organic covalent linkers between both π‐units involved in the dimerization (Scheme A) . Works carried out along these lines have led to the emergence of a wide range of responsive metamorphic molecular systems, the conformation of which can be controlled by redox input …”